Mixing apparatus

ABSTRACT

Apparatus for mixing solid material with a liquid wherein a mixer device comprising a casing and an impeller is mounted below an outlet at the bottom of a subsidiary vessel. Liquid and solid material are continuously supplied to the subsidiary vessel, separately or together. Material within the casing is expelled outwardly by the impeller and is subjected to thorough mixing and disintegration. Further material, drawn downwardly in the subsidiary vessel, is directed towards the mixer casing by inwardly and downwardly sloping side walls of the subsidiary vessel.

United States Patent Love 1 June 13, I972 [54] MIXING APPARATUS 2.6353594/1953 Dreyfus ..259/26 X i 2.882,l49 4/l959 Willemsm. ..259l66 X [72]E2532 3. 3,417,968 I2/l968 Schlecht .259/23 x 3.502.305 3/1970 Grun..259/8 [22] Filed: March 19, I969 Primary Eraminer-Waiter A. Scheel 1Appl' 808399 Assl'slant E.taminer-Alan I. Cantor Anorney- Delio &Montgomery [30] Foreign Application Priority Data March 25, 1968 GreatBritain ..l4,363/68 Amer Apparatus for mixing solid material with aliquid wherein a I52] U.b. LL... ..259/8, 259/96 i er device comprisinga casing and an impeller is mounted [51] Int. Cl. ..B0lf 7/26 be|ow anout) at the bonom f a subsidiaty vemL Liquid [58] new of "259/661 andsolid material are continuously supplied to the subsidiary 259/23 7vessel. separately or together. Material within the casing is expelledoutwardly by the impeller and is subjected to thorough [56] and mixingand disintegration. Further material, drawn UNITED STATES PATENTSdownwardly in the subsidiary VCSSQI, i8 directed IPWflIdB lllC 3 62 89I, 968 R h al 259/96 X mixer casing by inwardly and downwardly slopingslde walls of ,3 ,6 l 01 man et the subsidi vessel 3,423,075 H1969Knudsen et a]. ..259/96 X ary 3.489356 1/1970 Combs et al. ..259/96 X 13Claims, 2 Drawing Figures L\ I7 F 2, /I1

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INVENTOR Gordon U. Love,

D f Ms M W 1 w mma:

MIXING xrmnxrus BACKGROUND OF THE INVENTION This invention relates tomixing apparatus.

In mixing a powder with a liquid it is known to mount a mixing devicewithin a vessel containing the liquid and to apply a charge of thepowder to the surface of the liquid. Frequently, however, the powdertends to float on the surface of the liquid and difficulty isexperienced in wetting" the powder as a preliminary to its being mixedand dispersed throughout the volume of the liquid. it is found that theparticles of the powder coagulate, forming lumps which are wetted on theoutside but dry inside. These lumps float on the surface for a long timebefore they are drawn down by the vortex action of the mixing device.Unfortunately, however, the vortex also draws air or other surroundinggaseous medium into the volume of the liquid, and the greater thesurface area of the liquid the greater is the required vortex action andthe greater the amount of gaseous medium introduced.

in mixing a solid which is readily wetted with a liquid there is aproblem in ensuring that all of the solid is drawn through the mixingdevice and is thereby subjected to mixing and disintegration.Accordingly, it has been proposed to carry out the mixing in a pipelinewithin which there is provided an apertured partition wall and a mixingdevice which is arranged on the outlet side of the partition wall andreceives all of the material flowing through the aperture in the wall.Even with this apparatus solid material may separate out from the liquidon the inlet side of the partition wall and this may cause a blockage inthe pipeline.

STATEMENT OF THE INVENTION The present invention includes apparatus formixing solid material with a liquid, comprising a mixer casing having aninlet aperture and outlet aperture means, an impeller which is adapted,upon rotation, to expel material within the casing outwardly via theaperture means, thereby effecting mixing of the solid material with theliquid, and a subsidiary vessel having inlet means for the continuoussupply of liquid and solid material thereto and an outlet which, in useof the apparatus, is disposed in a lower part of the subsidiary vesseland provides a flow of liquid and solid material to the inlet apertureof the casing, the side walls of the subsidiary vessel being so arrangedthat material at each location within the subsidiary vessel is drawndownwardly within the vessel and is directed towards the inlet aperturein the casing upon rotation of the impeller.

Suitably, the mixer casing, the impeller, and the outlet of thesubsidiary vessel are disposed within a main vessel adapted to contain alarge volume of the said liquid and solid material, and the surface areaof liquid within the subsidiary vessel which is exposed to thesurrounding gaseous medium is substantially smaller than the exposedsurface area of liquid in the main vessel when the mixer casing andimpeller are immersed in the liquid in the main vessel, whereby solidparticles at each location on the surface of the liquid in thesubsidiary vessel are drawn downwardly by the impeller and areaccompanied by a reduced amount of the said gaseous medium.

Alternatively, an apparatus according to the invention further comprisesan inlet conduit for the continuous supply of liquid and solid materialto an upper part of the subsidiary vessel, and an outlet conduit intowhich material is expelled by the impeller via the outlet aperture meansin the mixer casing.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described,by way of example, with reference to the accompanying drawings, inwhich:

FIG. 1 is a vertical section of an apparatus according to the invention;

FIG. 2 is a side elevation of a second apparatus according to theinvention.

2 DESCRIPTION OF THE PREFERRED EMBODIMENTS The mixing apparatus shown inFIG. 1 of the drawings is suitable for use in mixing a powder such ascarboxymethyl cellulose with a large volume of a liquid such as waterwithout introducing undesirable quantities of air or other surroundinggmeous medium into the mixture.

This apparatus includes a main, cylindrical vessel 1 which serves as acontainer for the liquid and a small, subsidiary vessel 3 which ismounted within the main vessel 1 and is used for introducing the powderinto the liquid therein. Associated with the subsidiary vessel 3 aremixing devices 5 and 7, each including a casing and an impeller, and anelectric motor 9 for driving the impellers.

The subsidiary vessel 3 of the present apparatus has a cylindrical upperpart 11, a tapering intennediate part 13. and a lower neck part 15 ofreduced diameter. The vessel 3 is open at the top and bottom thereof.

For mounting purposes a horizontally extending bracket 17 is welded tothe top of the subsidiary vessel 3 and extends outwardly therefrom. inits mounted position the subsidiary vessel 3 is arranged with thebracket I7 resting on a peripheral rim 19 at the top of the main vessel1 and fixedly secured to the rim by suitable clamping means (not shown).The subsidiary vessel 3 then extends downwardly into the main vessel 1with the lower part 15, the intermediate part I3 and approximately halfof the upper part 11 of the subsidiary vessel below the surface of theliquid in the main vessel.

An inlet aperture 21 for liquid is formed in the cylindrical upper part11 of the subsidiary vessel 3 and is arranged below the level of liquidin the main vessel 1, as hereinafter described.

The above-mentioned mixer devices 5 and 7 are mounted at the lower endof the subsidiary vessel 3, each having a casing which is securedrelative to the vessel 3 and an impeller which is mounted on a shaft 23extending downwardly through the vessel 3, coaxially thereof. At itsupper end the impeller shaft 23 is coupled to an output shaft of theelectric motor 9, which is mounted on a cross-member 25 extendingdiametrically of the upper, open end of the vessel 3.

For mounting the casings of the mixer devices 5 and 7 a mounting ring 27is welded to the outside of the neck part 15 of the subsidiary vessel 3,coaxially thereof, and an annular mounting plate 29 having a diametergreater than the diameter of the ring 27 is secured to the undersurfaceof the ring by four screws 31.

A casing 33 of the upper mixing device 5 is formed of a cylindrical sidewall having an outer, peripheral flange which is secured to theundersurface of the mounting plate 29 by means of screws 35. The casing33 is arranged coaxially of the neck part 15 of the subsidiary vessel 3so that an open, upper end thereof receives material flowing downwardlyfrom that vessel. Outlet apertures 37 are formed in the cylindrical sidewall of the casing 33.

An impeller 39 of this first mixing device includes an annular plate 4|formed on its lower surface with an apertured boss and on the uppersurface thereof with four upstanding, radially extending blades 43. Theexternal diameter of the annular plate 41 and of the volume swept out bythe blades 43 upon rotation thereof is slightly less than the internaldiameter of the side wall of the casing 33 and the blades 43 arearranged at the same vertical location as the outlet apertures 37 inthat side wall. The inlet to the casing 33, which is defined by theannular space between the shaft 23 and the neck part 15 of the vessel 3,has a cross-sectional area substantially smaller than the crosssectional area of the volume swept out by the impeller blades.

For securing a casing 45 of the second mixer device 7 relative to thesubsidiary vessel 3 a cylindrical mounting element 47 is clamped betweenthe undersurface of the above-mentioned, annular mounting plate 29 and alower annular, mounting plate 49 by means of axially extending screws51, each screw 5| extending upwardly through an aperture in the plate 49and having its upper end threadably engaged in an aperture in the plate29. The cylindrical element 47 and the upper and lower annular plate 29and 49, respectively, together form a cylindrical chamber 53 into whichmaterial emerges from the casing 33 of the first mixer device 5.

The casing 45 of the lower mixing device 7 includes a cylindrical meshscreen 55 which is arranged coaxially of the lower annular plate 49 withan outer flange at the upper end of the screen 55 contacting theundersurface of the plate 49 and secured thereto by screws 57. Each ofthese screws 57 extends upwardly through a bottom wall in a housing 59which is also secured below the lower annular plate 49 and supports abearing 61 for the lower end of the impeller shaft 23. This housing 59is formed with a series of apertures 63 to allow material flowingthrough the mesh screen 55 to pass to the exterior of the housing.

An impeller 65 of the lower mixing device 7 is similar to the impeller39 of the upper device 5, having an annular plate 67 which is secured tothe impeller shaft 23 and four upstanding blades 69 disposed adjacent tothe mesh screen 55 forming the side wall of the casing 45.

Secured to the element 45 is a tube 71 which receives liquid flowingoutwardly through the mesh screen 55 and the apertures 63. An outlet ofthe tube 71 is disposed at a predetermined location in the main vessel1.

An additional impeller 73 is secured to the shaft 23, within thesubsidiary vessel 3.

in use of the present apparatus the main vessel 1 is filled with liquidto a level above the inlet aperture 21 in the side wall of thesubsidiary vessel 3 as described above. The electric motor 9 is thenenergized to rotate the impeller shaft 23 and the three impellersmounted thereon and, finally, the powder is fed into the upper end ofthe subsidiary vessel 3 at a predetermined rate.

Rotation of the bladed impeller 39 of the upper mixing device causesliquid and powder within the subsidiary vesel 3 to be drawn downwardlythrough the aperture at the lower end of the vessel and into the mixercasing 33. Downward flow of material is assisted by the rotatingimpeller 73. Material is expelled radially outwardly through theapertured side wall of the casing 33 and into the chamber 53 surroundingthis casing by the rotating impeller blades 43. In passing through thenarrow, annular gap between the blades 43 and the side wall of thecasing 33 the material is subjected to large shearing forces whicheffect thorough mixing and disintegration of the particles.

Fresh liquid flows into the subsidiary vessel 3 from the main vessel 1,via the inlet aperture 21, and fresh powder is supplied to the upper endof the vessel 3 as mentioned above.

Material entering the chamber 53 is drawn downwardly through the chamberby the action of the impeller 65 of the lower mixing device 7. Thematerial then passes into the casing 45 of the device 7 and is expelledoutwardly through the mesh screen 55 by the rotating impeller blades 69.From the screen 55 the material travels through the apertures 63 in thebearing housing 59 and into the tube 71, from which it travels into themain volume of liquid in the main vessel 1. The mixture is againsubjected to thorough mixing and disintegration in passing through thegap between the blades 69 of the impeller 65 and the mesh screen of thedevice 7.

The fact that the inlet to the casing 33 has a cross-sectional areasubstantially smaller than the cross-sectional area of the volume sweptout by the impeller blade 43 reduces the vortex action which wouldotherwise be exerted on material above the inlet to the casing 33.

in using the present apparatus, however, it is only necessary for theimpeller 39 to set up a small vortex action for powder to be drawndownwardly from all parts of the surface of the liquid in the vessel 3,since the downwardly tapering part 13 of the vessel 3 ensures that allof this powder is directed towards the device 5. The vortex action isnot sufficient to drawn down large quantities of air. Efficient mixingis therefore obtained without undue aeration of the mixture. If thesubsidiary vessel 3 were not present and the mixing device 5 were simplyimmersed in the liquid within the main vessel 1 it would only bepossible to draw powder from allparts of the liquid surface byincreasing the size or speed of rotation of the impeller 39. This wouldresult in undue aeration.

The mixing device 7 provides a second mixing of material from the firstdevice 5, the mesh screen 55 leading to a further reduction in particlesize. in cases where aeration can be tolerated the impeller 73, whoseposition on the shaft 23 is adjustable, increases the vortex action andprovides rapid wetting of large quantities of material.

It will be appreciated that the above apparatus can be modified byremoving the mixing device 7 and allowing material from the device 5 totravel directly into the liquid in the main vessel 1. Alternatively, oneor more further mixing devices may be provided below the device 7 so asto ensure even more mixing of material from the subsidiary vessel 3.Each of these further devices is provided with an inlet chamber whichreceives material flowing from the preceding device, in the manner ofthe above-described chamber 53 between the devices 5 and 7.

In another apparatus according to the invention a further mixing devicebelow the devices 5 and 7 has both its inlet and outlet communicatingwith the liquid in the main vessel 1. This further device thereforeprovides additional mixing of material already in the main vessel. Withthe subsidiary vessel 3 mounted at one side of the main vessel 1, asdescribed above, the provision of the further mixing device has thefurther advantage of causing a general circulation of liquid around themain vessel l, thereby improving dispersion of the solid particlesthrough the main vessel.

The impeller 73 can be replaced by a worm.

In the apparatus shown in FIG. 1. the subsidiary vessel 3 isapproximately 20 inches in diameter and has an overall depth ofapproximately 2 feet. The main vessel 1 has a diameter of approximately20 feet and a depth of approximately 20 feet. The volume of the mainvessel 1 is therefore approximately 700 times the volume of thesubsidiary vessel 3 and the surface area is approximately 150 times thatof the subsidiary vessel. It will be appreciated that the maximum sizeof subsidiary vessel 3, or the minimum value of the above ratios, whichwill give an acceptable result depends upon the amount of aeration whichcan be tolerated. In general, however, it would be expected thatalthough any reduction in surface area over which the powder isdispersed is desirable it would be usual to effect a reduction of atleast five times and preferably at least 10 to 20 times.

The apparatus shown in H6. 2 of the drawings is for use indisintegrating solid material and thoroughly mixing the material with aliquid.

This apparatus includes a subsidiary vessel 103 which corresponds to theabove-described vessel 3 except for the omission of the inlet aperture21 in the side wall of vessel 3. Mounted below the subsidiary vessel I03are mixing devices 105 and 107 respectively corresponding to theabove-mentioned mixing devices 5 and 7. Each of these devices 105 and107 includes a mixer casing and an impeller which is mounted on a shafi109, driven by an electric motor 1 l I.

The subsidiary vessel 3 and the mixing devices 105 and 107 are disposedbetween an upper, inlet conduit [13 and a lower outlet conduit 115.

Liquid and solid material flow into the open top of the vessel 103 fromthe inlet conduit 113 and the mixing devices 105 and 107 are immersed inliquid in the outlet conduit 115.

in use of the present apparatus, liquid and solid material arecontinuously supplied to the vessel 103 from the conduit "3. Rotation ofthe impellers in the device I05 and 107 expels material through thecasings of these devices, causing thorough mixing and disintegration ofthe solid material. From the device 107 the mixture of liquid and solidmaterial is ex pelled into conduit 115. Material in the vessel 103 isdrawn downwardly by the impeller in the device 105, the downwardlytapering section of the vessel 103 ensuring that material at eachlocation in the vessel is directed towards the outlet at the bottom ofthe vessel.

It will be appreciated that the apparatus of FIG. 2 can be provided withseparate feed lines for liquid and solid material.

I claim:

1. Apparatus for mixing solid material with a liquid, comprising asubsidiary vessel having at least one inlet in an upper part thereof andan outlet in a lower part thereof, a first mixer casing which is formedwith an inlet in an upper end wall thereof and with outlet aperturemeans in a generally cylindrical side wall thereof, said outlet aperturemeans extending around said side wall, means for securing said casing tothe subsidiary vessel so that all material flowing downwardly throughthe outlet in the subsidiary vessel enters said casing whilst materialflowing outwardly from the outlet aperture means of said casing isprevented from returning to the subsidiary vessel via the outletthereof, an impeller shaft, and a first impeller mounted on the saidshaft and disposed within said casing, said impeller comprising agenerally circular plate formed with a plurality of upstanding impellerblades, with their radially outer ends adjacent to the side wall of thecasing, whereby, upon rotation of the shaft, the impeller forcesmaterial in said casing radially outwardly through the outlet aperturemeans, thereby subjecting the material to thorough mixing anddisintegration, wherein the side walls of said subsidiary vessel arearranged such that material therein is directed to said inlet to saidcasing, and wherein said inlet to said casing has a cross-sectional areasubstantially smaller than the cross-section of the volume swept out bysaid first impeller, thereby to produce a reduced vortex action onliquid in said subsidiary vessel and to draw solid material at anylocation within said subsidiary vessel downwardly into the said casing,without undue aeration of the material, to replace the expelledmaterial.

2. Apparatus as claimed in claim 1, wherein the subsidiary vessel has apart which tapers downwardly towards the outlet thereof.

3. Apparatus as claimed in claim 1, wherein said first impeller ismounted on a shaft which extends downwardly through the subsidiaryvessel and additional impeller means are provided on the shaft, abovesaid first casing and within the subsidiary vessel, for assisting indriving liquid and solid material downwardly towards said mixer casing.

4. Apparatus as claimed in claim 1, wherein said impeller shaft extendsbelow said first mixer casing, and a second impeller is mounted on saidshaft below said first mixer casing, and the said second impeller beingdisposed within a second mixer casing.

5. Apparatus as claimed in claim 4, wherein the outlet aperture means insaid first casing opens into a chamber having an outlet at a lower endthereof, the second mixer casing has an inlet aperture arranged toreceive material flowing downwardly through the said outlet, and thesecond impeller is adapted, upon rotation, to draw material within thechamber downwardly into the second mixer casing and to expel materialoutwardly through aperture means therein.

6. Apparatus as claimed in claim 5, including means for securing saidsecond casing to said chamber so that all material forced outwardlythrough said outlet aperture means of said first casing is preventedfrom returning to said first casing.

7. Apparatus as claimed in claim 4, wherein said mixer casings, saidfirst and second impellers, and the outlet of the subsidiary vessel aredisposed within a main vessel adapted to contain a large volume of thesaid liquid and solid material, and the surface area of liquid withinthe subsidiary vessel which is exposed to the surrounding gaseous mediumis substantially smaller than the exposed surface area of liquid in themain vessel when the mixer casings and impellers are immersed in theliquid in the main vessel.

8. apparatus as claimed in claim 7, wherein the subsidiary vessel, mixercasings and impellers are offset from a central position relative to themain vessel, as viewed in plan.

9. Apparatus as claimed in claim 7, wherein material expelled from theaperture means in the mixer casings is conveyed via a tube to apredetermined location in the main vessel.

10. Apparatus as claimed in claim I, wherein said impeller shaft is theoutput shaft of an electric motor which is mounted above the subsidiaryvessel.

ll. Apparatus as claimed in claim 1, wherein a single inlet is providedin said subsidiary vessel for supply of both liquid and solid materialto said vessel.

12. Apparatus as claimed in claim 1, wherein said outlet of saidsubsidiary vessel and said inlet to said first mixer casing areconnected by a neck portion.

13. Apparatus as claimed in claim 22, wherein said neck portion iscylindrical and the diameters of said neck portion and said inlet areequal.

1. Apparatus for mixing solid material with a liquid, comprising asubsidiary vessel having at least one inlet in an upper part thereof andan outlet in a lower part thereof, a first mixer casing which is formedwith an inlet in an upper end wall thereof and with outlet aperturemeans in a generally cylindrical side wall thereof, said outlet aperturemeans extending around said side wall, means for securing said casing tothe subsidiary vessel so that all material flowing downwardly throughthe outlet in the subsidiary vessel enters said casing whilst materialflowing outwardly from the outlet aperture means of said casing isprevented from returning to the subsidiary vessel via the outletthereof, an impeller shaft, and a first impeller mounted on the saidshaft and disposed within said casing, said impeller comprising agenerally circular plate formed with a plurality of upstanding impellerblades, with their radially outer ends adjacent to the side wall of thecasing, whereby, upon rotation of the shaft, the impeller forcesmaterial in said casing radially outwardly through the outlet aperturemeans, thereby subjecting the material to thorough mixing anddisintegration, wherein the side walls of said subsidiary vessel arearranged such that material therein is directed to said inlet to saidcasing, and wherein said inlet to said casing has a crosssectional areasubstantially smaller than the cross-section of the volume swept out bysaid first impeller, thereby to produce a reduced vortex action onliquid in said subsidiary vessel and to draw solid material at anylocation within said subsidiary vessel downwardly into the said casing,without undue aeration of the material, to replace the expelledmaterial.
 2. Apparatus as claimed in claim 1, wherein the subsidiaryvessel has a part which tapers downwardly towards the outlet thereof. 3.Apparatus as claimed in claim 1, wherein said first impeller is mountedon a shaft which extends downwardly through the subsidiary vessel andadditional impeller means are provided on the shaft, above said firstcasing and within the subsidiary vessel, for assisting in driving liquidand solid material downwardly towards said mixer casing.
 4. Apparatus asclaimed in claim 1, wherein said impeller shaft extends below said firstmixer casing, and a second impeller is mounted on said shaft below saidfirst mixer casing, and the said second impeller being disposed within asecond mixer casing.
 5. Apparatus as claimed in claim 4, wherein theoutlet aperture means in said first casing opens into a chamber havingan outlet at a lower end thereof, the second mixer casing has an inletaperture arranged to receive material flowing downwardly through thesaid outlet, and the second impeller is adapted, upon rotation, to drawmaterial within the chamber downwardly into the second mixer casing andto expel material outwardly through aperture means therein.
 6. Apparatusas claimed in claim 5, including means for securing said second casingto said chamber so that all material forced outwardly through saidoutlet aperture means of said first casing is prevented from returningto said first casing.
 7. Apparatus as claimed in claim 4, wherein saidmixer casings, said first and second impellers, and the outlet of thesubsidiary vessel are disposed within a main vessel adapted to contain alarge volume of the said liquid and solid material, and the surface areaof liquid within the subsidiary vessel which is exposed to thesurrounding gaseous medium is substantially smaller than the exposedsurface area of liquid in the main vessel when the mixer casings andimpellers are immersed in the liquid in the main vessel.
 8. apparatus asclaimed in claim 7, wherein the subsidiary vessel, mixer casings andimpellers are offset from a central position relative to the mainvessel, as viewed in plan.
 9. Apparatus as claimed in claim 7, whereinmaterial expelled from the aperture means in the mixer casings isconveyed via a tube to a predetermined location in the main vessel. 10.Apparatus as claimed in claim 1, wherein said impeller shaft is theoutput shaft of an electric motor which is mounted above the subsidiaryvessel.
 11. Apparatus as claimed in claim 1, wherein a single inlet isprovided in said subsidiary vessel for supply of both liquid and solidmaterial to said vessel.
 12. Apparatus as claimed in claim 1, whereinsaid outlet of said subsidiary vessel and said inlet to said first mixercasing are connected by a neck portion.
 13. Apparatus as claimed inclaim 12, wherein said neck portion is cylindrical and the diameters ofsaid neck portion and said inlet are equal.